I. Field of the Invention
The present invention relates to a passive system and corresponding methods for efficiently and economically determining real time range and/or altitude of a signal emitting target.
II. Description of the Prior Art
Passive surveilance systems are known which can identify the bearing or azimuth of a target by simply rotating a receiving antenna and determining the azimuth angle of that antenna upon receipt of a signal transmitted by the target. In order to effectively utilize such target azimuth information, additional target identification data, such as range or altitude, must be associated or fused with the azimuth information.
Passive systems are known which can provide range and/or altitude information. For example, a Passive Ranging on Non-Scanning Emitters (PRONSE) system is known which requires two or more widely separated sensors such as sensors on each wing tip of a system carrying aircraft. In the PRONSE system, it is necessary to know the location and altitude of each sensor with respect to the other with a great degree of precision. The flexibility of large aircraft structures mandates the use of auxiliary locating systems, such as inertial or laser systems, to track the relative movement of the sensors.
Another type of system capable of identifying range and/or altitude is known as a Time Delay of Arrival (TDOA) system in which a receiver calculates the difference in transit time between a signal received directly from a target and that signal received as a reflected wave. In addition, the receiver determines the depression angle of the directly received signal and/or reflected signal by measuring the physical position of the antenna at the time of receipt. Such systems have a substantial disadvantage of introducing significant error due to the inability to accurately measure the depression angle by measuring the angle of the receiver antenna.
A single platform passive ranging system using altitude comparison is also known today. However, this system requires a detailed knowledge of emitter power characteristic and relies upon the assumption that the strength of the recorded signal from the target is indicative of the range of that target. This system is not reliable due to the fact that emitters are seldom adjusted for maximum operational performance, and atmospheric anomolies can significantly alter the received signal amplitude.
In view of the foregoing, it is an object of the subject invention to provide a passive surveilance system and related methods whereby range and/or altitude can be readily obtained for fusion with other data such as azimuth angle data.
Another object of the subject invention is to provide a system and related methods for determining real time range and/or altitude using hardware and software which is less costly than that presently required.
A still further object of the present invention is to provide a single platform passive ranging system and related methods, which will work for all signal emitting targets, including jammers, but yet which are affordable and technically feasible.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.